Energy storage devices are needed for wide application with regenerative energy sources such as those that utilize the sun and the wind. These storage devices are useful in matching a varying energy supply to a varying energy demand. Furthermore, possibilities are being sought that allow for energy storage in decentralized facilities for load equalization. In both cases lead storage batteries can be used. However, this type of cell has several disadvantages including relative expense, physical weight and a low energy density.
A new type of energy storage devices which can be used for the mentioned purposes is the hydrogen/bromine cell (see: "J. Electrochem. Soc.", vol. 127 (1980), pages 549 to 555). In this cell, the electrolysis of hydrobromic acid (HBr) is utilized for storing the electric energy: ##STR1##
In the HBr electrolysis, hydrogen (H.sub.2) and bromine (Br.sub.2) are generated and are stored separately. When needed, they are converted again into hydrobromic acid in order to obtain electric energy, specifically, in a fuel cell reaction (see, for instance: "Energy", vol. 4 (1979), pages 61 to 66). The advantage of the hydrogen/bromine system as compared to other corresponding systems such as hydrogen/oxygen is the high reversibility of the bromine electrode.
In hydrogen/bromine cells known, graphite often is used as cell frame material. These cells however have the disadvantage that bromine diffuses through the cell frames.